The invention relates to rolls and in particular to apparatus and methods for detecting bowing of a roll used in contact with hot material and reducing any bowing detected. This is particularly useful in the manufacture of glass ribbon from a mass of molten glass where glass is caused to flow between co-operating rolls and it is necessary to prevent excessive bowing of the rolls in order to achieve glass ribbon of uniform thickness.
In the known rolled plate process for manufacturing a glass ribbon, glass is caused to flow from a mass of molten glass to a passage between co-operating rolls. The shape and separation of the rolls determine the surface shape and thickness of the glass ribbon being formed. As the rolls are in contact with hot glass, the rolls themselves will become heated and difficulties can arise from bowing of the rollers. To avoid these difficulties it is necessary to detect any bowing and then selectively adjust the temperature of parts of the roll surface to compensate for any bowing detected. It is an object of the present invention to provide improved apparatus for detecting any bowing and to apply corrective thermal treatment to selected areas on the roll surface. It is a further object to provide an improved electrical control arrangement which initiates thermal correction only when bowing of the roll exceeds a predetermined limit.